A. Field of Invention
The present invention relates generally to diaphragm valves and more particularly to diaphragm valves used to control flows of fluids that are chemically aggressive and corrosive or that are required to be free of contamination caused by reaction with valve materials.
B. Description of Related art
Diaphragm valves are available for controlling the flow of fluid media including chemically aggressive and corrosive fluids. The general design and operation of diaphragm valves can be seen in U.S. Pat. No. 3,349,795, U.S. Pat. No. 4,596,268, U.S. Pat. No. 3,628,770 and U.S. Pat. No. 4,609,178. Of the mentioned valves all except U.S. Pat. No. 4,609,178 are symmetrical thereby providing for functioning independent of the direction of the flow of the fluid media. Of the bidirectional diaphragm valves only the valve described in U.S. Pat. No. 4,596,268 entitled "Diaphragm Valves For Corrosive Liquids" is specifically adapted for the control of corrosive fluid media but all operate in essentially the same manner. Such valves generally function by providing a flexible diaphragm which is attached to a plunger or other means such that the diaphragm is biased toward a valve seat closing the flow passage and thereby impeding flow. For example, in the valve described in U.S. Pat. No. 4,596,268, the biasing means is attached to the diaphragm by means of a bolt or other attaching device which is imbedded in or integrally molded to a backing diaphragm as well as a sheet of inert material covering the surface exposed to the fluid media. The diaphragm in U.S. Pat. No. 4,596,268 is thus repeatedly subjected to opposing forces at the point of attachment of the biasing means as well as radial tension and flexion caused by the forcible operation of the biasing means when opening and closing the valve.
A number of other valve devices have been advanced for the control of corrosive fluids without using the means of a flexible diaphragm, for example, U.S. Pat. No. 4,260,130 U.S. Pat. No. 4,580,593 U.S. Pat. No. 4,214,730 and U.S. Pat. No. 4,399,834. The functional characteristics and sealing mechanics of these valves is entirely dissimilar from the characteristics of the diaphragm valve advanced herein.
When a diaphragm valve is used to control the flow of chemically aggressive fluids, the entire wetted surface of the valve, including the diaphragm, must be made of corrosion resistant material to avoid deterioration. Similarly, when such a valve is used to control the flow of fluids that are sensitive to contamination such as in medical or scientific applications, inert materials must be used in the manufacture of the valve body and diaphragm.
Currently available materials suitable for use in the diaphragm under such conditions include, elastomeric polytetrafluoroethylene (PTFE) substances. A diaphragm which is shaped or molded of these materials to provide for the attachment of a biasing means is more expensive than a simple disc cut or stamped from sheet stock. In addition, a diaphragm adapted to attachment to a biasing means is difficult to install or replace, particularly in miniature applications required in systems handling minute quantities of reagents, substrate and other fluid media, particularly such systems being developed in medical, biochemical and biotechnical fields.
As illustrated by the requirement of a backing diaphragm to provide support for the inert diaphragm shown in U.S. Pat. No. 4,596,268, the characteristic forcible opening and closing of a conventional diaphragm valve can cause diaphragm failure particularly when the components are selected for their chemically inert characteristics rather than their mechanical properties. The available inert materials are also known to take a compression set when forcibly deformed as in the conventional valve.
The existing diaphragm valves are designed for installation in a straight run of piping so that the inlet and outlet valves extend along the same line but opening in opposite directions, a configuration which, among other things, creates difficulties in constructing a bank of multiple control valves in a compact configuration. Such valves also characteristically use a valve seat of a width that is approximately equal to the diameter of the flow passage in general. In applications where flow capacity restriction is undesirable, for the area of a transverse section of the flow passage to remain relatively constant over the valve seat when the valve is open, the portion of the diaphragm engaging the valve seat must travel a distance approximating the diameter of the flow passage in general.